This invention relates to a planetary gearbox and a robotic joint having a planetary gearbox.
Designing robotic joints for harsh remote environments, such as outer space, presents a number of design challenges. For example, typically, there are strict energy budgets. Consequently, the energy requirements for a motor motivating a joint must be as small as possible. On the other hand, the portion of the robot below the joint may have a significant inertial mass so that a large torque is required to drive it according to specifications. In order to meet these conflicting design criteria, a high ratio gearbox is typically provided between the motor and the lower portion of the robot.
Because of the cost of delivering robotic components to a remote environment, these components are designed to be as small and lightweight as possible. A light weight also reduces inertial forces of the robot, in use. These requirements extend to the joint gearbox: it too should be as small and lightweight as possible. The gearbox must also be able to withstand the temperatures of the harsh environment; for space or planetary applications, this means withstanding very low, or very high, temperatures.
A robot typically has a number of joints, each powered by a motor. Each joint may have different torque and input to output ratio requirements. This suggests different gearboxes for different joints; this provides further design complexity and increased manufacturing costs.
Accordingly, a need remains for a gearbox which may provide a high capacity and a high ratio and which may be made so as to be lightweight, miniature, and robust. Such a gearbox would be suitable for use in a robot deployed in a harsh remote environment. A need also remains for such a gearbox designed to accommodate different ratios and capacities in order to minimize complexity and manufacturing cost.
A joint may have a multi-stage planetary gearbox between the stationary housing and the rotary housing. To accommodate different gear ratios, the rotary housing may be joined to the stationary housing by a releasable attachment. This allows portions of the planetary gearbox to be replaced so that, for instance, the last stage may be chosen as either a simple or compound differential planetary stage. To allow for different capacities, a quotient of a sum of all teeth of a sun gear of a stage and of the ring gear with which the planetary gears of the stage mesh to both the number three and the number four yields an integer. In this way, the stage may be provided with either three or four planetary gears. The gearbox may have a ring gear common to a plurality of simple planetary stages. Where the final stage is a simple planetary stage, the carrier may be provided with a flange extending around, and bearing mounted to, the common ring gear. To reduce weight and increase robustness, the planetary gears of a stage are retained on their carrier by a bumper ring provided between carriers. An angle sensor may be provided between the stationary and rotary housings.
According to the present invention, there is provided a joint comprising: a stationary housing; a rotary housing joined to said stationary housing by a releasable attachment, said releasable attachment permitting said rotary housing to rotate relative to said stationary housing; a motor carried by said stationary housing; a multi-stage planetary gearbox having a first stage sun gear motivated by said motor, said gearbox terminating at said rotary housing, such that, by releasing said releasable attachment, said rotary housing, and at least a portion of said multi-stage planetary gearbox, may be removed.
According to another aspect of the invention, there is provided a planetary gearbox having a sun gear meshing with three or four planetary gears where a quotient of a sum of all teeth of said sun gear and of a ring gear with which said planetary gears mesh to both the number three and the number four yields an integer value.
According to a further aspect of the invention, there is provided a planetary gearbox having a sun gear meshing with a given number of planetary gears where a quotient of a sum of all teeth of said sun gear and of a ring gear with which said planetary gears mesh to both of two adjacent integer values, where one of said adjacent integer values is said given number, yields an integer value.
According to another aspect of the invention, there is provided a planetary gearbox having a plurality of simple planetary stages with a common ring gear such that said common ring gear, in unison with planetary and sun gears of said gearbox, provides radial stability to said planetary and sun gears without need for an axle.
According to a further aspect of the invention, there is provided a planetary gearbox, comprising: a bumper ring extending between a first carrier for a sun gear and a second carrier for planetary gears meshing with said sun gear, said bumper ring being rotatable at least with respect to said second carrier, said bumper ring overlapping with said planetary gears in order to retain said planetary gears on said second carrier.
According to a yet further aspect of the invention, there is provided a planetary gearbox, comprising: a bumper ring overlapping with an end face of all planetary gears meshing with a single sun gear so as to retain said planetary gears.
According to a yet further aspect of the invention, there is provided a planetary gearbox having a plurality of simple planetary stages with a common ring gear, a final stage of said simple planetary stages having a carrier with a flange extending around, and bearing mounted to, said common ring gear.
Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following description in conjunction with the following figures.